[clangd] Don't miss the expected type in merge.

[ilya-biryukov]

LGTM, thanks!

clang-tools-extra/trunk/clangd/index/Merge.cpp

Symbol mergeSymbol(const Symbol &L, const Symbol &R) {
   if (S.Signature == "")
     S.Signature = O.Signature;
   if (S.CompletionSnippetSuffix == "")
     S.CompletionSnippetSuffix = O.CompletionSnippetSuffix;
   if (S.Documentation == "")
     S.Documentation = O.Documentation;
   if (S.ReturnType == "")
     S.ReturnType = O.ReturnType;
+  if (S.Type == "")
+    S.Type = O.Type;
   for (const auto &OI : O.IncludeHeaders) {
     bool Found = false;
     for (auto &SI : S.IncludeHeaders) {
       if (SI.IncludeHeader == OI.IncludeHeader) {
         Found = true;
         SI.References += OI.References;
         break;
       }

clang-tools-extra/trunk/unittests/clangd/IndexTests.cpp

TEST(MergeTest, Merge) {
   R.CanonicalDeclaration.FileURI = "file:///right.h";
   L.References = 1;
   R.References = 2;
   L.Signature = "()";                   // present in left only
   R.CompletionSnippetSuffix = "{$1:0}"; // present in right only
   R.Documentation = "--doc--";
   L.Origin = SymbolOrigin::Dynamic;
   R.Origin = SymbolOrigin::Static;
+  R.Type = "expectedType";
 
   Symbol M = mergeSymbol(L, R);
   EXPECT_EQ(M.Name, "Foo");
   EXPECT_EQ(StringRef(M.CanonicalDeclaration.FileURI), "file:///left.h");
   EXPECT_EQ(M.References, 3u);
   EXPECT_EQ(M.Signature, "()");
   EXPECT_EQ(M.CompletionSnippetSuffix, "{$1:0}");
   EXPECT_EQ(M.Documentation, "--doc--");
+  EXPECT_EQ(M.Type, "expectedType");
   EXPECT_EQ(M.Origin,
             SymbolOrigin::Dynamic | SymbolOrigin::Static | SymbolOrigin::Merge);
 }
 
 TEST(MergeTest, PreferSymbolWithDefn) {
   Symbol L, R;
 
   L.ID = R.ID = SymbolID("hello");